Fiber optic cables are currently being used throughout the aerospace and communications industries. These cables are typically employed in computerized equipment and communications applications where space and/or weight restrictions make traditional copper wiring systems inappropriate. Optical fiber, as a data transfer means, is known for its exceptional speed and bandwidth capability and for its ability to provide reliable communication signals in systems that generate large amounts of electromagnetic radiation.
The commercial and military aerospace industry is a harsh testing ground for fiber optic cables, requiring flawless performance in extremely demanding physical environments. In such environments, where even minor failures can result in loss of life and property, fiber optic cables are subjected to conditions which include destructive extremes in vibration, shock, temperature, pressure, water/chemical emersion, as well as electromagnetic and radio frequency interference. It is for these reasons that aerospace standards for the manufacture and supply of fiber optic cables are some of the most rigorous found in any industry.
The world's major aerospace manufacturers conduct aggressive ongoing research on new designs and materials that can deliver stronger, lighter and more durable fiber optic cables.
U.S. Pat. No. 6,233,384 B1 to Sowell, III et al. provides one such new design. By way of this reference, a ruggedized fiber optic cable is provided wherein a fluoropolymer first jacketing material is applied over a buffered optic fiber core. A rigid, closely-spaced, spirally or helically wrapped wire layer is applied over the first jacketing layer, followed by the application of a mechanical braid (e.g., plastic fibers or strands) over the wire layer. To protect the fiber optic cable from the environment, an outer jacket (e.g., tetrafluoroethylene/(perfluoroalkyl) vinyl ether copolymer) is applied over the mechanical braid. Although this cable design provides some protection for the optic fiber core, the outer jacket will shrink in the axial direction during cable manufacture and use, thereby increasing stress on the optic fiber core, which can cause the fibers to crack or break.
U.S. Pat. No. 5,615,293 to Sayegh discloses a fiber optic cable assembly that employs acrylic coated optical fibers surrounded by a buffer material such as foamed fluorinated ethylene-propylene (FEP). The acrylic coating material on the optical fibers, however, has a use temperature ranging from about −65° C. to about 125° C. and will degrade when the FEP buffer material is extruded onto the fibers, causing undesirable yellowing and even loss of integrity of the coating material.
Accordingly, it is a general object of the present invention to avoid the above-referenced disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a fiber optic cable that serves to minimize or eliminate shrinkage stress on the optic fiber core.
It is a more particular object to provide a fiber optic cable having improved dimensional stability that demonstrates more stable signal carrying characteristics in extremely demanding physical environments.
It is another more particular object to provide a fiber optic cable that employs one or more intermediate layers that serve to protect the buffered optical fiber(s) from the effects of high temperature during cable manufacture and use.